Method of making abrasive articles



May 8, 1945.

F. A. UPPER 2,375,263

METHOD OF MAKING ABRASIVE ARTICLES Filed June 27, 1944 IN V EN TOR.

v fiasofe/cz 4 (/PPEe BY Patented May 8, 1945 METHOD OF'MAKING ABRASl-VEARTICLES Frederick A. Upper, Niagara Falls, N. Y., asslgnor to TheCarborundum Company, Niagara Falls, N. Y., a corporation of DelawareApplication June 21,;1944, Serial No. 542.324

8 Claims. (on. 51-297) This invention relates to the manufacture ofabrasive articles. More particularly it relates to methods of makingresilient abrasive articles of the bonded type such as grinding andpolishing wheels, discs, blocks, pads, sticks and other shapes having amild or soft" abrading action and formed of a composite of feltedfibrous sheets having abrasive grain, and usually an adhesive bindertherefor, included internally of the fibrous sheets. The inventionespecially pertains to improved methods of making such abrasive articlesfrom a plurality of superimposed flexible,

\ fibrous abrasive-containing sheets or web material whereby thefinished article is more facilely and quickly formed and in which theresultant product is characterized by a more uniform density andhardness grade throughout together with a mild or soft abrasive actionwhich combines an effective cutting rate with an efficient andsatisfactory polishing action. c

There has always been a need for abrasive articles of the bonded typewhich would combine an effective cutting action with satisfactoryfinishing r polishing whereby a reasonable amount of material would beremoved from the -work.being abraded and at the same time the articlewould be left with a desirable surface finish or polish. Abrasivearticles heretofore provided for such dual purposes have failed to becompletely satisfactory in accomplishing both goals and have been foundto be defective in one respect or another. Among the reasons for theirunsatisfactoriness have been the failure to combine an appreciabledegree of cutting ability with a resilience or softnessiof cuttingaction, nonhomogeneity of the abrasive article, lack of permanency ofthe abrasive content (i. e., failure of the abrasive wheel structure toretain the abrasive particles within the abrading body),

non-uniformity of abrasive action, inflexibility,

etc. Provision of satisfactory properties in one respect has usuallybeen at a sacrifice of one or more of the other characteristicsdesirable in such products.

Ordinary bonded abrasive articles of the prior art consisting ofabrasive grains and a binder therefor in which various fibers have beenincorporated for reinforcing means or for other purposes, on account oftheir harsh, hard cutting behavior, have never been found suitable forthe purposes herein set forth; They do not provide an action equivalentor comparable to the combined "soft cutting and polishing action of thepresent articles.

Recently, abrasive articles having a combined cutting and polishingaction have been made from a plurality of felted fibrous abrasivecontaining sheets superimposed one on the other and adhesively orotherwise secured in position for grinding and polishing use. Sucharticles and methods of-making them have been set forth and described inUnited, States Patent No. 2,355,667, issued August 15, 1944. Accordingtothe procedure described therein abrasive wheels and other shapes areformed by cutting pieces of the abrasive-containing fibrous material ofthe size and shape of the desired article from the roll ofabrasive-included web material and assembling them, directly to form thedesired article. While the resultant articles have shown a cuttingaction of the desired type, the methods of making them have been fraughtwith numerous procedural dimculties which -make it extremely difficultto carry out the operation efficiently and efiectively, especially on alarge or commercial scale. to produce articles of uniformcharacteristics not only throughout each individual article but also toprovide large numbers of articles having uniformity of abradingcharacteristics from article to article. The making of smaller wheelsand shapes has presented specific additional problems involved in thehandling of large numbers of small pieces of th loose sheet material.

r I have discovered improved methods of making the aforesaid articleswhereby the above men tioned and other dimculties are obviated and bywhich large numbers of abrasive wheels and other shapes can beefiiciently and quickly fabricated regardless of size and shape andwhich will be not only uniform throughout each individual article but inwhich such uniformity in cutting characteristics can be repeatedlyobtained and controlled in large numbers of articles in accordance withthe results desired. The herein. described methods, by reason of theincreased rate of production made possible and the improved uniformityof product obtained thereby, results in economic savings as well as theaccrual of other advantages all of which will become used in forming oneof the compressed slabs is preferably determined by weighing. Theseslabs can be further processed immediately or stored indefinitely forlater processing. The abrasive and adhesive content of the fibrousmaterial is incorporated and distributed throughout the fibrousweb atthe time of its manufacture and constitutes an integral part thereof.This fibrous abrasive web material can be satisfactorily made in anumber of ways, as will be set forth later. ing fibrous sheet materialhas some adhesive included therein which may suffice for the making ofcertain abrasive articles, an additional adhe'sive usually, andpreferably, is incorporated with the fibrous sheet material, as a sizingapplied to one or both sides-of the abrasive included sheet materialprior to its initial consolidation into slabs, whether in its originalroll form or after it has been cut into large sheets for forming thecompressed slab stock.

The above compressed slab stock is then died out on a punch press or bysimilar mechanism, or cut or punched out by hand, to provide a number ofsmaller rings, discs or other shaped pieces, the shape depending uponthe specific article to be made therefrom. One or more of the smallerpieces is then subjected to a further consolidating operation as, forexample, by molding under heat and pressure to mature or set theadhesive binder and form the desired abrasive article. After a finaldressing or edging operation in accordance with customary practice thearticle is ready for use.

In order to better understand the nature of the invention reference ismade to the accompanying drawing in which:

Figure 1 is a top plan view of a single compressed slab composed of anumber of sheets of superimposed, felted, fibrous. abrasive-containingweb material made in accordance with the first step of the presentprocess and shows the manner in which smaller shapes are died or outfrom the slab.

- Figure 2 is an enlarged fragmentary, vertical cross-section throughthe line 11-11 of Figure 1, and

Figure 3 is a diagrammatical, vertical crosssection through an abrasivewheel made in accordance with the present invention.

The abrasive-included fibrous web material used in making the productsof the present invention can be manufactured in several ways. A verysatisfactory method of making included abrasive sheet material of theherein required type is that set forth and fully described in U. S.Patents Nos. 2,284,715 and 2,284,716.- Briefly, the ,felted fibrous webis formed by feeding a plurality of thin carded fibrous membranes from anumber. of carding assemblies onto a moving endless support so that eachmembrane is deposited or superimposed upon the preceding membranes untila web of loosely felted fibrous material of the desired thickness isbuilt up on the traveling support. A number of abrasive grain hoppersare also disposed between the carding assemblies and above the travelingconveyor. Abrasive grain is fed from the hoppers onto the fibrousmembranes at various stages in the building up of the final web, sothat, as a result, the abrasive material is applied betweenthe'individual membranes making up the web and so is internallydistributed throughout the fibrous web. A suitable adhesive binder isthen incorporated within the fibrous abrasive web and Although theabrasive-containthe web is consolidated to a desired density and passedto a curing zone, where the adhesive is matured or set. The includedabrasive web is then wound into rolls for use as a source material forthe manufacture of the products herein described.

In practicing the invention, any of the abrasive materials in common usemay be employed, such as silicon carbide, diamonds, boron carbide, fusedaluminum oxide, flint, corundum, emery, rouge and similar substances.The size of the abrasive particles may vary from the finest polishing orbufiing powders to the coarser grit sizes used in grinding.

Other methods of incorporating abrasive material internally of thefibrous sheet material during its manufacture may be employed. Forexample, the abrasive particles can be thoroughly admixed with theadhesive binder and the mixture applied to the uncompacted web by theusual adhesive-applying rolls. This method has been found to beparticularly satisfactory for the inclusion of the finer abrasivematerials of the .terial into the web or sheet after it has been builtsize employed in bufilng and polishing operations.

Another method is to project the abrasive maup to the desired thicknessand immediately prior to consolidating the web. The projection of grainis suitably carried out by means of a blast of air or gas against one orboth surfaces of the fibrous web, the ar stream being laden with theabrasive material to be included internally of the web. The other stepsin the formation and consolidation of the web are carried out in amanner simitions from the-web. For a more complete descriptlon of such aprocess and product; reference is made to U. S. Patents Nos. 2,284,738and 2,284,739 in which further details are also given of the aboveprocedures for including abrasive materials within the fibrousstructures.

Abrasive included sheet material of the herein required type can also bemade by wet-felting procedures employing the various types of paperstockfibers and including abrasive therein at the time of making the sheetmaterial. One satisfactory method of making the abrasive included sheetmaterial by said wet-felting procedure is that set forth and fullydescribed in co-pending application Serial No. 461,139. filed October'I, 1942.

Briefly, the felted fibrous paper stock material having abrasive grainincorporated internally thereof is made by first forming a liquid,usually aqueous, suspension of fibrous material, the fiber content ofthe suspension being very low and in the neighborhood of 0.5 to 5% ofthe suspension, collecting the fibrous suspension on a suitable support,introducing abrasive grains with or without an adhesive binder into thefibrous web while it is in a highly aqueous, or fiuid condition,extracting the water or other liquid medium from the web, and furtherdrying and compacting the web to the desired density. Optionally,theabrasive grains can be given a preliminary coating of ture.

In one such modification the fibrous suspension of paper-stock isdeposited upon a foraminous support in one step and the abrasive grainis de-' posited in several increments while the web is still in a highlyaqueous or fluid condition. That portion of abrasive applied firstpenetrates deepest into the web structure, and the abrasive of eachsucceeding deposition penetrates the web to a lesser degree by reason ofthe continually decreasing amount of water present and the consequentthickening of the fibrous body. The distribution of abrasive within theweb can thus be controlled by variation of the amounts and places ofdeposition during the dewatering or the web so as to obtain any desiredeffect;

In a modified form of the process a fluid fibrous suspension iscollected upona plurality of revolving foraminous supports, such ascylinders, which are partially immersed in the fibrous suspensloni Thethin fibrous membranes collected upon the foraminous supports are thensuccessively transferred to a common carrier, usually a moving endlessfelt blanket or belt, in superimposed relationship to form a fibrous webstruc- Abrasive grain is incorporated into the fibrous web structure bydeposition or projection between and into thevarious-individualgmembranes as they are deposited on the carriersupport. This method has the advantage that, since the fibroussuspensions can be varied, the co position or structure of variousportions of the web can be varied if desired. Adhesive binders can beincorporated in the fibrous web, regardless of the procedure used, atvarious stages in the process, such as by inclusion in the fibroussuspension, introductlon during dewatering of the web, with the abrasivegrains as a coating thereon, or after the web has been substantiallydewatered and prior to the final compacting and drying of the web.

A still further modification which can be used to make fibrous abrasivematerials is the process of forming a wet fibrous abrasive lap bya-cylinder wet-press process, in which a fibrous suspen= sion similar tothat used in the cylinder method above is fed, usually from a singlecylinder mold,"

onto a traveling wet felt carrier belt. The thin fibrous membrane isconveyed over one or more suction boxes to remove a portion of the waterand passed between a pair of pressure rolls. As the fibrous materialpasses between the pressure rolls it is transferred to the upperpressure roll upon which it is wound in a series of successive layersuntil the desired thickness of fibrous material is obtained, whereuponthe material is removed by hand or by a suitable knife or doctor blade.Abrasive grain isfed onto the fibrous sheet previous to its passagebetween the pressure rolls and is thereby incorporated within thefibrous structure.

Another satisfactory method of making abrasive included paper-stock webmaterial is that set forth and fully described in co-pending applicationSerial No. 461,140, filed October 7, 1942.

In accordance with the process therein set forth, fibrous paper-stockabrasive sheet material is made from an aqueous suspension of around 3%fiber content in which the fibers are distributed in the suspensionassubstantially individu- I "3 ally separated fibers. This fibroussuspension is agitated, beaten, or otherwise mechanically treated, withsumcient vigor to render the fibers partially gelatinous, abrasive grainbeing incorporated in the suspension to the desired extent. A

sufilclent amount of abrasive grain is added to provide an abrasivegrain content of over and preferably 60-70% or more by weight of thefinal product after the water has been extracted.

The agitation of the fibrous suspension previous to and/or during theaddition of abrasive grain is very important in preparing a liquid inwhich the abrasive particles will remain uniformly in 1 suspension. Thisstability of suspension is believed to be due, at least in part, to theadherence of the abrasive particles to the partially gelatinized fibers.The amount of agitation or beating of the fibrous suspension necessaryto provide a suitable stable mixture of abrasive and fiber of the properconsistency depends upon the size of the abrasive particles. Forexample, a very slight agitation serves the purpose when the finestabrasive polishing powders are used whereas with the useof 60 or 80 gritabrasive grains, it is desirable to subject the suspension to a muchlonger and/or more vigorous agitation. Suspension of the abrasiveparticles may be assisted by incorporating an adhesive in-the fluidmass. either consistency has'been prepared as above outlined,

it is flowed or otherwise deposited on a suitable foraminous support inthe form of a continuous, highly aqueous layer from whichthe water orother liquid suspending medium is extracted, and the resultingfilm isfurther dried and compacted to the desired density. These operations canbe performed by flowing the suspension onto a moving endlesswire screenor by collecting a plurality of thin membranes onto cylinder molds andtransferring themto a suitable felt blanket in superimposed relation toform a web of the desired thickness. While it is usually desirable toproceed in the described manner of forming continuous fibrous webs bythis particular method the process can be practiced in modified form byus- Modifying agents such as waterproofing compounds, anti-frictionagents, fiexibilizers, plasticizers and other fillers may beincorporated in the web at the time oi' making irrespective of theparticular procedure followed, in order to render the web resistant towater or impart other specific desirable properties to all or certaincontrolled portions of the web.

Abrasive included felted fibrous web material such as that made by anyone of the aforementioned'methods is used as a source of raw materialfor the making of abrasive articles in accordance with the presentinvention. As a. specific example of the manner in which the presentprocfibrous sheet material.

' slabs.

ese has; been carried out and an abrasive article made in accordancewith the present invention, the following procedure is given;-

A flexible, felted fibrous sheet material made in accordance with theteachings of U. 8. Patents Nos. 2,284,738 and 2,284,739, and containingap proximately 75% of fused alumina particles of 80 mesh grit size.cotton fibers and 10% natural rubber derived from latex is sized with aaqueous solution of a casein glue (such as that made and sold under thetrade-mark name of Casco by Casein Corporation of America) to provideabout 10% casein by weight based on the The roll of adhesively sizedabrasive included fibrous sheet material is cut into the form orlargedndlvidual sheets as, for example, in the shape of theparallelogramshaped slab shown in Figure l, a slab size convenient forhandling being approximately 28" long by 13" wide. It has been foundthat in the use of the slabs in the making of disc-shaped articles suchas grinding wheels and polishing wheels and the like that if the acuteinner angle of the parallelogram is 60 there is a minimum of wastageentailed in cutting the material for use. Although the fibrous abrasiveweb is preferably sized with adhesive on one or both sides in roll formdue to the convenience of handling, it can, if desired, be sized afterit has been cut into individual sheets; also the process is notrestricted to the specific size or shape of sheet set forth as othersizes and shapes can be employed to suit the particular conditions andequipment available and the type and size of abrasive article to bemade. A sufficient number of the adhesively coated sheets are assembledin superimposed position to provide a slab of specified thickness as,for example, A" thick when compressed as by cold pressing. The number ofindividual sheets to be used in forming one of the compacted slabs visdetermined by weighing. In the case of forming the slab l illustrated inFigures 1 and 2 a number of abrasive included felted fibrous sheets 5,which have been previously sized on one side with an adhesive coating 6consisting of a 20% aqueous solution of casein glue to the extent ofabout 10% casein by weight of the fibrous sheet material, are assembledin superimposed relation and cold pressed at a' pressure of 4000 poundsper square inch. The pressing operation is usually carried out on anumber of slabs simultaneously by the use of either a multiple platenpress or by the insertion of steel plates between the various groups ofsheet material forming the The pressures employed are adequate to forcethe sheet material together so firmly that the resulting slab can beconveniently handled as a single piece although the sheets are notstrongly bonded together nor is the adhesive usually permanently set orcured atthis. point in the process. It has been found satisfactory insizing the sheet material to apply the adhesive solution to only oneside of the sheet material, although if desired the adhesive can beapplied to both faces; also, in assembling the sheet material when theadhesive is applied to only one side of the sheet material the differentsheets are preferably arranged either with the adhesively coated sidesfacing inwardly toward the center of the assembly or with the adhesivelycoated sides all facing in one direction. The slab fragment depicted inFigure 2 in enlarged form shows the former arrangement. The thickness ofeach slab is controlled and held to a predetermined figure by means ofstop blocks inserted between the press platens.

Referring further to the drawing, Figure 3 shows a cross-sectional viewthrough an abrasive wheel I formed from a single disc-shaped segment ofthe slab material such as that shown in Figures 1 and 2. The initiallycompressed slab of Figure 1 shows a number of disc shaped segments 8removed from the slab for the fabrication of abrasive wheels. A singledisc-shaped segment 8 cut from the slab 4 shown in Figure 1 andconsisting of a number of layers or abrasive-included, adhesively-coatedfelted fibrous sheet material 5 is placed in a hot press and subjectedto apressureof 1700 pounds per square inch and-a temperature of 260 F.for 15 minutes. The hot pressed wheel is then removed from'the press andcooled after which the central arbor hole 9 is punched out on a punchpress and the wheel placed in an oven for 5 hours at 260 F. to completethe curing of the bond. The temperature, pressure and period of pressingis varied depending upon the size and shape of the specific articlebeing made. The article, after the oven cure, is dressed and edgedaccording to the usual procedure. When only a single, (1180-. shapedsegment is used, the resulting abrasive wheel is usually one ofapproximately thlck nes's. Thicker wheels are formed by superimposingone or more additional disc shaped segments upon the first segment andhot pressing the several discs of slab material to combine the severaldiscs and compress the material to the desired density. In formingabrasive wheels and like articles having central arbor holes in which ithe article has afinal thickness greater than They are applicable tocarrying out the present invention and, in fact, they constitute thepre-' ferred method of obtaining the final consolidation and formationof the abrasive article. Briefly, the piece or pieces of slab materialfrom which the grinding wheel or other abrasive shape is to be formedare placed between two layers of heavy cloth which have been previouslysaturated with water and the excess water removed as by squeezingbetween a pair of rubber rolls. A suitable fabric is heavy, close-wovencanvas or duck although other woven or felted fabric ma- I above.

process, as for example the grade of hardness, can be altered byvariations in the quantity and character of the adhesive binder employedin making the abrasive-containing, fibrous'sheet mate It has been foundthat the character of the abrasive articles produced by theherein-described rial, and also by the choice of auxiliary orsupplementali' adhesive substance which is admixed with the sheetmaterial as a size thereto. It is desirable that the adhesives selectedfor making the articles do not smear during grinding operations. This isespecially true in polishing wheels and devices where smearing of thebond tends to produce a hot cutting or burning action which is ruinousto the finish being produced.

Among those substances which can be satisfactorily used as bondingmaterials herein in addition to the specific adhesive sizing compositionset forth above, and which are non-smearing, are

included glue adhesives, particularly when treated with plasticizingagents such as ethylene glycol, sorbitol, glycerine and the like. Theplasticizer may amount to as much as 40% by weight of the total adhesivebinder. Other non-smearing adhesives which can be used are casein glues,natural or synthetic rubber latices, urea resins, phenol aldehyde resinsand other natural or. synthetic resins, or mixtures of two or more ofsuch adhesives.

The herein-described invention offers numerous improvements andadvantages over the prior art.

It provides a practical method of fabricating abrasive articles such asgrinding and polishing wheels, stones and the like, having a soft orresilient combined cutting and polishing action.

The articles of the present invention have a relatively high rate ofstock removal from the material being ground and at the same timeproduce a surface finish equal to that obtained by an ordinary bondedabrasive article embodying abrasive particles several grit sizessmaller. Abrasive products made as herein described out both efiicientlyand effectively, with an accompanying polishing action, and are capableof being used at high operating speeds without chattering, operatingsmoothly to remove burrs and produce very high finishes on metalcastings. It is theorized that the soft" cutting action of such abrasivearticles is the result of the abrasive grains being cushioned bythesurrounding felted fibers and binder so as to prevent gouging andscratching and to provide the abrasive grains witha yielding backgroundby which they are caused to maintain individually more effective contactwith the work and at the same time absorb and take up inequalities ofsurface so as t not to scratch or mar the surface being finished.

Although I have set forth, in the specific example, certain specificconditions, it will be understood that my invention is not limited tothe conditions there described. The length of time that the article issubjected to heat and pressure is determined to some extent by thethickness of the article being molded, but is usually in the range of.15 to minutes. Likewise, articles of different grades can be made byvarying the fiber, abrasive and adhesive content of theabrasivecontaining felted fibrous material, the amount and kind ofadhesive applied thereto as a size, and by the density to which thearticles are compacted. In general the sheet material contains 5-20%adhesive, 5-20% fibers, usuallycotton, and 65-90% abrasive.

Having described andset forth the invention in detail, the scope of theinvention is not to be confined other than by the appended claims.

Iclaim:

1. The method of making bonded abrasive articles from a plurality ofsuperimposed layers of abrasive-included, felted, fibrous sheet materialwhich comprises assembling a number of sheets of previously sizedabrasive-included fibrous web material in superimposed relation,subjecting said assembled sheets to an initial consolidating action toform therefrom a compressed slab of the desired thickness, cutting outpieces of the desired size and shape from the said compressed slabs, andfurther consolidating said out out pieces of compressedslab material toform abrasive articles of the desired thickness.

2. The method of making bonded abrasive articles from a plurality ofsuperimposed layers of abrasive-included, felted, fibrous sheet materialwhich comprises assembling a number of sheets of previously sizedabrasive-included, fibrous web material in superimposed relation,subjecting said assembled sheets to an initial consolidating action toform therefrom a compressed slab of the desired thickness, cutting outpieces of the desired size and shape from the said compressed slabs, andfurther consolidating said out out pieces of compressed slab material bymeans of heat and pressure to form abrasive articles of the desiredthickness,

3. The method of making bonded abrasive articles from a plurality ofsuperimposed layers of abrasive-included, felted, fibroussheet'inaterial which comprises applying an adhesive coating to. asurface of an abrasive-included, fibrous web material in roll form anddrying the same, cutting large sheets from the adhesively-coated webmaterial, assembling a number of the sized sheets of abrasive-included,fibrous web material in superimposed relation, subjecting said assembledsheets to an initial consolidating action to form therefrom a compressedslab of the desired thickness, cutting out pieces of the desired sizeand shape from the said compressed slabs, and further consolidating saidout out pieces of com pressed slabmaterial to form abrasive articles ofthe desired thickness. 1

4. The methodof making bonded abrasive articles from a plurality ofsuperimposed layers of abrasive-included felted, fibrous sheet materialwhich comprises cutting a number of large sheets from the abrasiveincluded fibrous, web material, applying an adhesive coating to asurface of said sheets, assembling a number of the adhesivelycoatedsheets of the abrasive-included, fibrous web material in superimposedrelation andthen subjecting said assembled sheets to an initial consolidating action to form therefrom a compressed slab of the desiredthickness, cutting out pieces of the desired size and shape from thesaid compressed slabs, and further consolidating said cut out pieces ofcompressed slab material to form abrasive articles of the desiredthickness.

5. The method of making bonded abrasive articles from a plurality ofsuperimposed layers of abrasive-included, felted, fibrous sheet materialwhich comprises assembling a number of sheets of previously sizedabrasive-included; fibrous.

web material in superimposed relation, cold pressing said assembledsheets to form therefrom a compressed slab of the desired thickness,cutting out pieces of the desired size and shape from the saidcompressed slabs, and further consolidating said out out pieces ofcompressed slab material by means of heat and pressure to form abrasivearticles of the desired thickness.

6. The method of making bonded abrasive articles-from a plurality ofsuperimposed layers of abrasive-included, felted fibrous sheet materialwhich comprises assembling a number of sheets of previously sizedabrasive-included, fibrous web material in superimposed relation, coldpressing said assembled sheets at an approximate pres- 'sure of 4000lbs. per square inch to form therefrom a compressed slab oi the desiredthickness,

v which comprises assembling a number of sheets or previously sizedabrasive-included, fibrous web material in superimposed relation, coldpressing said assembled sheets to form therefrom a compressed slab ofthe desired thickness, cutting out pieces or the desired size andshapetrom the said compressed slabs, and hot pressing the cut out piecesof the compressed slab material to form abrasive articles of the desiredthickness.

8. The method of making bonded abrasive articles from a plurality ofsuperimposed layers or abrasive-included, felted, fibrous sheet materialwhichcomprises assembling a number of sheets oi previously sizedabrasive-included. fibrous web material in superimposed relation.subjecting saidassembled sheets to an initial consolidating action toform therefrom a compressed slab of the desired thickness, cutting outpieces of the desired size and shape from the said compressed slab,assembling in superimposed relation a suificient number 01 the cut outpieces of initially compressed slab material to provide an abrasivearticleot the desired thickness when permanently compacted, and furtherconsolidating the superimposed pieces oi compressed slab material siredabrasive article.

. FREDERICK A. UPPER.

egos

by means of heat and pressure to form the de-

